JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Critical Thinking

  • question_answer
    A sodium atom is in one of the states labeled 'Lowest excited levels'. It remains in that state for an average time of 10?8 sec, before it makes a transition back to a ground state. What is the uncertainty in energy of that excited state

    A)            6.56 ´ 10?8 eV                       

    B)            2 ´ 10?8 eV

    C)            10?8 eV                                    

    D)            8 ´ 10?8 eV

    Correct Answer: A

    Solution :

                       The average time that the atom spends in this excited state is equal to Dt, so by using \[\Delta E.\,\Delta t=\frac{h}{2\pi }\] Þ Uncertainty in energy\[=\frac{h/2\pi }{\Delta t}\]  \[=\frac{6.6\times {{10}^{-34}}}{2\times 3.14\times {{10}^{-8}}}=1.05\times {{10}^{-26}}J=6.56\times {{10}^{-8}}eV\]


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